Vertebroplasty is a procedure during which bone cement, biomaterials, and/or other flowable compounds are delivered into a vertebra. A syringe or other delivery device is generally provided within which the bone cement to be delivered is stored shortly before the bone cement is to be delivered. For example, the delivery device may include a barrel or housing including an open inlet end and an exit end with a narrow outlet. A plunger or threaded driver may be advanced into the inlet end to force bone cement within the barrel out the outlet in the exit end.
A cannula may be inserted percutaneously through the cutaneous layers of tissue above a hard tissue structure being treated and into the hard tissue structure. For example, the hard tissue structure may be a vertebra, and the cannula may include a sharpened tip to penetrate through cortical bone and into the cancellous bone within the vertebra. Alternatively, the hard tissue structure may be exposed using conventional surgical procedures before inserting the cannula and/or the cannula may be inserted over a needle previously placed or simultaneously advanced into the vertebra.
A semi-rigid or flexible tube, e.g., twenty to fifty centimeters long, may be connected between the proximal end of the cannula and the outlet of the delivery device to deliver bone cement via the tube into the hard tissue structure. The tube may be bent slightly during the procedure, e.g., to keep the user's hands and/or the delivery device out of the field of an imaging device, such as a fluoroscope, that may be used to monitor the procedure.
Alternatively, the syringe may be connected directly to the proximal end of the cannula. Such a rigid connection, however, requires a user to support the syringe/cannula combination, which may expose the user to x-ray radiation, e.g., from a fluoroscope used to monitor the injection of the material as it is being injected, requiring the user to wear appropriate additional x-ray protection, which may be cumbersome and inconvenient.
In addition, because of the high viscosity of bone cement, high pressures are generally required to inject bone cement from the delivery device, through the tube and cannula, and into the hard tissue structure. For example, pressures of up to one to three thousand pounds per square inch (1,000–3,000 psi) may be required to inject bone cement from the delivery device. This requires the user to apply substantial force, while simultaneously supporting the weight of the delivery device and its contents. This may cause fatigue of the user and/or undesired movement of the cannula delivery device during the procedure.
Accordingly, apparatus and methods for delivering bone cement or other compounds into vertebrae would be useful.